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Re: URIEquivalence-15

From: <Misha.Wolf@reuters.com>
Date: Mon, 29 Apr 2002 16:00:13 +0100
Message-ID: <T5a8ee1a012c407b70691c@reuters.com>
To: Norman Walsh <Norman.Walsh@Sun.COM>
Cc: www-tag@w3.org

On 29/04/2002 14:59:38 Norman Walsh wrote:
> As I've said before, I think the only practical URI comparison
> algorithm is "lexicographic identity". But every time I've said that,
> I've had this nagging concern about how to deal with characters that
> might or might not be escaped.
>
> There's an erratum to XML[1] that tries to tackle a related issue, but
> the IRI draft[2] (I haven't read it with great care, so I could be
> overlooking something) seems to provide a more complete algorithm for
> "normalizing" the possibly escaped characters in a URI.
>
> I'm now inclined to say that the right way to compare URIs is to turn
> them into IRIs and test their lexicographic identity.

In general, one can't reliably transform a URI into an IRI, as the
character encoding is not known.  So I suspect that your initial
inclination was correct.  IRIs do come into the picture in two respects:

1.  The rule for identity should address IRIs as well as URIs.  Indeed,
    as every URI is by definition an IRI, it need only address IRIs :-)

2.  Because lexicographic identity generally results in an IRI not
    matching the corresponding URI, it is important that specs,
    designers and software follow this rule (given in IRI draft):

| 2.3.1 When to convert from IRIs to URIs
|
|   The mapping from IRIs to URIs SHOULD only be applied when necessary,
|   and as late as possible.

This agrees with the XML spec[3]:

| Since escaping is not always a fully reversible process, it must be
| performed only when absolutely necessary and as late as possible in a
| processing chain. In particular, neither the process of converting a
| relative URI to an absolute one nor the process of passing a URI
| reference to a process or software component responsible for
| dereferencing it should trigger escaping.

> [1] http://www.w3.org/XML/xml-V10-2e-errata#E4
> [2] http://www.ietf.org/internet-drafts/draft-duerst-iri-00.txt

[3] http://www.w3.org/XML/xml-V10-2e-errata#E26

Misha





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Received on Monday, 29 April 2002 11:02:13 GMT

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